Low molecular weight siloxanes with one functional group

ABSTRACT

Low molecular weight siloxane materials having one functional group are provided which have reduced tendency to form phase separated domains after polymerization. Two classes of siloxane materials are included: (1) symmetric siloxane macromonomers containing at least two monomer termini and one polymerizable functional group which is equidistant from the termini, and (2) assymetric siloxane macromonomers having at least one polymerizable functional group terminus and at least one oxygen-containing polar hydrophilic terminus selected from the group consisting of hydroxyl, ether, and polyether. Symmetric siloxane macromonomers having hydroxyl termini are useful for forming biocompatible materials, such as for contact lenses, tissue regeneration scaffold polymers, and coatings to reduce non-specific binding of proteins.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 60/914,436, filed Apr. 27, 2007, the disclosure of whichis herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Polydimethylsiloxanes, polyalkylmethylsiloxanes and fluorinatedalkylmethylsiloxanes are well known for their hydrophobicity. In avariety of applications it is desirable to incorporate dimethylsiloxaneunits into other macromolecular structures in order to increase oxygenpermeability, release, emollient, or low temperature properties, but agreater degree of hydrophilicity is required in the final polymercompositions. For example, methacrylate functional polysiloxane-basedstructures can be utilized in pigment dispersion, lithographic, releasecoating and contact lens applications.

Often, functional low molecular weight polysiloxanes, such as amethacryloxypropyl functional polydimethylsiloxane or3-methacryloxy-2-hydroxypropyl functional polydimethylsiloxane, arecopolymerized with monomers such as methyl methacrylate (MMA) or morepolar monomers, such as hydroxyethylmethacrylate (HEMA),glycerylmethacrylate acrylonitrile, dimethylacrylamide, orvinylpyrrolidone. If the polysiloxane domain is too large, particularlywith polar monomers, molecular phase separation can occur, reducingmechanical properties or, in cases such as hydrated copolymers, yieldingcompositions that are cloudy and are not suitable for opticalapplications. On the other hand, reducing the number of siloxane unitsto prevent phase separation can make desirable properties, such as thoseassociated with oxygen permeability or surface energy, unachievable.

However, tightly controlled structures with distinct molecular weightscan be utilized to achieve these properties by providing the maximumnumber of siloxane units which do not cause phase or domain separationin the final polymer. More specifically, macromonomers (alternatelydenoted macromers), polymers having molecular weights of less than 5000,that contain one polymerizable group, such as methacrylate, acrylate,3-methacryloxy-2-hydroxypropyl, or vinyl on the alpha and/or omegaposition of a polydimethylsiloxane have been the preferred startingmaterials for many pigment dispersion, lithographic and contact lensapplications. These macromonomers are formed either directly byterminating an anionic non-equilibrium ring opening polymerization ofcyclosiloxanes with a functional chlorosilane, such asmethacryloxypropyldimethylchlorosilane, or through intermediates formedby termination with dimethylchlorosilane and then functionalizing byhydrosilylation or additional synthetic steps. This type ofpolymerization is sometimes referred to as living anionic ring-openingpolymerization or “living AROP.”

For example, monomethacryloxy-terminated polydimethylsiloxane can beformed by initiating the “living” polymerization ofhexamethylcyclotrisiloxane with n-butyl lithium and quenching thereaction with methacryloxypropyldimethylchlorosilane.3-Acryloxy-2-hydroxypropyl terminated polydimethylsiloxane can be formedby initiating the “living” polymerization of hexamethylcyclotrisiloxanewith n-butyl lithium, quenching the reaction with dimethylchlorosilanefollowed by hydrosilylation with allylglycidyl ether, and finally addingacrylic acid catalyzed by a metal salt such as chromium acetate. Thus,the products of current art are low molecular weight polysiloxanes witha functional group at one terminus and a hydrophobic group derived fromthe anionic initiator, typically a butyl or methyl group. Patentsdescribing methods which use these macromers as comonomers include U.S.Pat. Nos. 5,166,276; 5,480,634; 5,016,148; 5,179,187; 5,719,204; and7,052,131.

Most efforts on “living” AROP have been dedicated to forming blockco-polymers, as reviewed by I. Yilgor in Advances in Polymer Science,86, 28-30 (1988). C. Frye and others at Dow Corning made the earliestreports on living AROP (see J. Org. Chem., 35, 1308 (1970)).Monomethacryloxypropyl terminated polydimethylsiloxanes produced by“living” AROP, such as the compound shown in structure (I), were firstintroduced to the US market in Silicon Compounds Register & Review, 4thedition, R. Anderson, B. Arkles, G. Larson Eds. Petrarch Systems, p. 271(1987).

These materials are offered for sale under the trademarks MCR-M11 andMCR-M17 by Gelest Inc. (Morrisville, Pa.). Recent reviews by J.Chojnowski, in “Silicon Compounds: Silanes and Silicones” (B. Arkles, J.Larson, Eds, Gelest, p. 389-405 (2004) and G. Belorgney and G. Sauvet in“Silicon Containing Polymers” (R. G. Jones, Ed; Kluwer, p. 43-78 (2000))generally refer to this class of materials as ω-monofunctionalpolysiloxanes.

The general synthetic technique utilized in the prior art is to initiatea living polymerization of a ring-strained cyclotrisiloxane with analkyllithium or lithium alkyldimethylsilanolate initiator and, aftercyclic siloxane monomer is consumed, terminate the reaction via acapping reaction. In other variations, different monomers are fed to theliving polymer before termination, or the living polymer may be doubledin molecular weight by coupling with a non-functional material, such asdimethyldichlorosilane.

Monofunctional materials are usually formed directly or indirectly by acapping reaction, i.e., in the case of methacrylate terminatedmaterials, either capping with methacryloxypropyldimethylchlorosilane,as described in U.S. Pat. No. 5,672,671, assigned to Chisso, or by firstforming a monohydride-terminated material by capping withdimethylchlorosilane and then performing hydrosilylation withallylmethacrylate. Additionally, monoepoxy terminated compounds, such asthose reported in U.S. Pat. No. 4,987,203, assigned to Chisso, have beenreacted with methacrylic acid to form 3-methacryloxy-2-hydroxypropylterminated polydimethylsiloxanes. The expected alternate route achievedby hydrosilylating a hydride terminated polydimethylsiloxane withallyloxyhydroxypropylmethacrylate has also been demonstrated by Parakkaet al (see WO 2006/102050). Examples of amino-termination andfunctionalization are provided by Leir et al in U.S. Pat. No. 5,237,082and Letchford in U.S. Pat. No. 6,031,060. While other monofunctionalmaterials have been reported, such as J. Pickering, et al (U.S. Pat. No.7,074,488), this technology does not yield linear materials that aremonodisperse, but are analogous to what are generally referred to asmonofunctional T-resins in silicone technology.

BRIEF SUMMARY OF THE INVENTION

A symmetric siloxane macromonomer according to the invention comprisesat least two monomer termini and one polymerizable functional group,wherein the polymerizable functional group is located equidistant fromthe at least two monomer termini.

An asymmetric siloxane macromonomer according to the invention comprisesat least one polymerizable functional group terminus and at least oneoxygen-containing polar hydrophilic terminus selected from the groupconsisting of hydroxyl, ether, and polyether.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, low molecular weight (less thanabout 20,000 Daltons, more preferably less than about 10,000 Daltons)polyalkylmethylsiloxanes are provided that have less tendency to formphase separated domains after polymerization than the monoalkylmonofunctional asymmetric macromonomers of the current art. For thepurposes of this disclosure, it should be understood that the terms “lowmolecular weight polymer,” “macromonomer,” and “macromer” aresynonymous. The macromonomers according to the invention may besymmetric or assymetric and all contain one polymerizable functionalgroup. As described in more detail below, in the symmetricmacromonomers, the polymerizable functional group is located equidistantfrom the monomer termini. In the asymmetric macromers, the polymerizablefunctional group represents one of the monomer termini.

Preferably, the macromonomers (both symmetric and asymmetric) accordingto the invention have molecular weights of less than about 20,000Daltons, more preferably less than about 10,000 Daltons, most preferablyabout 500 to about 5,000 Daltons. The backbones of the asymmetric andsymmetric siloxane macromers may be substituted or unsubstitutedpolyalkylmethylsiloxanes, including polydimethylsiloxanes, fluorinatedpolyalkylmethyl siloxanes, polydiphenylsiloxanes andpolyphenylmethylsiloxanes. It is also within the scope of the inventionto have backbones which contain different “blocks”, such asdimethylsiloxane blocks alternating with fluorinated polyalkylmethylsiloxane blocks.

The asymmetric and symmetric siloxane macromoners according to theinvention may be formed by polymerizing (via lithium counter-ioninitiated living anionic ring opening polymerization) cyclosiloxanes(cyclic monomers) with linear ether, cyclic ether, sulfoxide orformamide promoters and then terminating with functional groups or, inthe most preferred embodiments, coupling the living polymers, therebyforming symmetric rather than asymmetric macromonomers. The initiatorreacts with the strained cyclic monomer, opening it to create a tightion pair. The promoter then allows reaction, presumably thoughcomplexation or coordination of the ion pair with additional strainedcyclic monomers.

There are many possible permutations and combinations of materialspossible within the scope of this invention. Initiators which may beutilized include substituted and unsubstituted alkyl and aryl lithiumreagents such as, but not limited to methyl lithium, n-butyl lithium,methoxypropyl lithium, t-butyldimethylsiloxypropyl lithium, phenyllithium, methoxyphenyl lithium, p-t-butyldimethylsiloxyphenyl lithium,p-(bis(trimethylsilylamino)phenyl lithium, lithiumphenyldimethylsilanolate, lithium methacryloxypropyldimethylsilanolate,etc. Less effective initiators, such as lithium trimethylsilanolate andphenyl sodium, can also be used, but these are not as effective ingenerating monodisperse living chains.

Cyclic monomers (cyclosiloxanes) may include, for example,hexamethylcyclotrisiloxane, hexaethylcyclotrisiloxane,triphenyltrimethylcyclotrisiloxane,tris(trifluoropropyl)trimethylcyclotrisiloxane,methoxypropylpentamethylcyclotrisiloxane, etc. The monomers may be usedsingly to produce homopolymers or in combination to produce blockcopolymers.

Coupling reagents for the preparation of symmetric macromonomers whichare appropriate may include virtually any di- or tri-chloro, fluoro,bromo or iodosilane. Preferred reagents includemethacryloxypropylmethyldichlorosilane,acryloxypropylmethydichlorosilane, acrylamidopropylmethyldichlorosilane,vinylmethyldichlorosilane, methacryloxypropyltrichlorosilane, andvinyltrichlorosilane, which lead directly to functional macromers;methyldichlorosilane, bromobutylmethyldichlorosilane, and[(chloromethyl)phenethyl]methyldichlorosilane, which can be converted tomethacrylate functional macromers; or aminopropylmethyldifluorosilaneand (N-methylaminopropylmethyldifluorosilane), which can be derivatizedreadily to form, for example, acrylamidopropyl functional polymers.Other potential coupling agents include(vinylphenyl)methyldichlorosilane and (styrylethyl)methyldichlorosilane.

In preferred embodiments of the invention, the initiator ismethoxypropyl lithium, t-butyldimethylsiloxypropyl lithium, orp-t-butyldimethylsiloxyphenyl lithium; the cyclic siloxane ishexamethylcyclotrisiloxane ortris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane; and the quenchingor coupling reagent is methacryloxypropylmethyldichlorosilane oracryloxypropylmethyldichlorosilane. The ratio of initiator to cyclicsiloxane may be integral, such as 1:1, 1:2, or 1:3 if monodispersivityis desired, or non-integral if monodispersivity is not a requirement. Inthe cases of the t-butyldimethylsiloxypropyl lithium or thep-t-butyldimethylsiloxyphenyl lithium initiators, thet-butyldimethylsiloxy group may be removed in a subsequent syntheticstep to form a hydroxypropyl terminated polymer. The reaction may beperformed in non-coordinating solvents, such as cyclohexane, incoordinating solvents, such as tetrahydrofuran, or, with an appropriatepromoter, the reaction may be run without solvents (neat).

Using such reagents, it is within the scope of the invention to preparesymmetric macromonomers having polymerizable functional groups selectedfrom, but not limited to, vinyl, methacryloxyalkyl, acryloxyalkyl,arylamidoalkyl, styryl, hydrogen, and glycidoxyalkyl. The monomertermini may be non-polar and hydrophobic, such as alkyl (methyl, butyl,etc.) and aryl groups, or polar and hydrophilic, such as, but notlimited to, hydroxyl, ether, and polyether groups. These polar groupsprovide the macromonomer with the desirable properties describedpreviously and make them attractive for the production of biocompatiblematerials.

Assymetric siloxane macromonomers according to the invention preferablycontain at least one polymerizable functional group terminus and atleast one oxygen-containing, polar hydrophilic terminus preferablyselected from the group consisting of hydroxyl, ether, and polyether.Specific groups which may be included as the polymerizable functionalgroup termini have been described above.

Without wishing to be bound by theory, the reduction of the tendencytoward phase separation is thought to be from two factors: theintroduction of a relatively hydrophilic ether or hydroxyl group derivedfrom the initiator; and the fact that, in the preferred symmetricembodiment, the dimethylsiloxane block is smaller at equivalentmolecular weights than an equivalent traditional asymmetricmacromonomer. The reduction of the tendency to phase separate in aqueousmedia may be associated with the fact that the symmetric monomers havesmaller hydrodynamic volumes than their asymmetric equivalents. Thiseffect is more significant at low molecular weights. The symmetricmacromonomer may be visualized as centering the functionality on thepolydimethylsiloxane and “bisecting” the polydimethylsiloxane chainrather than terminating it, thus creating pendants at half its molecularweight.

It is also within the scope of the invention to prepare a macromonomercomprising more than two monomer termini. For example, a trifunctionalmonomer may couple three “living” polymers. In this case, symmetry maybe conceptualized as having a single chain bisected by the couplingmolecule and one of the residues of the three “living” polymers, i.e.,the center point of the chain has a functional pendant and a pendant ofsiloxane. The symmetric nature of the polymers may also be achieved byintroducing a second substitution at the central part of themacromonomer, as shown, for example, in structure (II), in which themacromonomer has three monomer termini.

Both the asymmetric and symmetric macromonomers according to the presentinvention differ from materials of the art. For example, a polarinitiator, such as methoxypropyl lithium, t-butoxypropyl lithium, ormethoxyethoxypropyldimethylsilanolate lithium, may be utilized, and thereaction may be terminated by a capping reagent, such asmethacryloxypropyldimethylchlorosilane, so as to produce an asymmetricmacromer with structure (III), for example, having a polymerizablefunctional group terminus and a polar hydrophilic terminus.

Alternatively, a single functionality may be introduced by a couplingreagent, such as methacryloxypropylmethyldichlorosilane, so as toproduce the symmetric macromer having structure (IV), for example, inwhich the polymerizable functional group is equidistant from the twomonomer termini. In a preferred embodiment, a polar initiator is used incombination with a coupling reagent.

The impact on relative hydrophilicity and the impact on phase separationin hydrophilic domains is dramatic for low molecular weight siloxanes.One explanation is that a nominal 1000 Dalton molecular weightmacromonomer has about 10-12 repeating siloxane groups. It is generallyconsidered that six or more dimethylsiloxane groups have an ability toform hydrophobic domains very readily due, not only to the low surfaceenergy associated with the dimethylsiloxane groups, but also to theflexible siloxane backbone which facilitates rapid conformationalrearrangement. By placing a relatively polar group at the center of themacromonomer rather than at the terminus, the domain size is held to 5-6siloxane groups and the facility for conformational rearrangement isreduced. The introduction of polar end-groups further reduces theability for chain ends to associate by hydrophobic interaction.

In a preferred embodiment of this invention, a symmetric macromonomerwith hydroxyl groups at both ends, as shown in structure (V), providesan excellent balance of oxygen permeability, reactivity with comonomersand hydrophilicity compatible with most hydrophilic polymer systems.Monomers of this type are valuable in contact lenses, tissueregeneration scaffold polymers, and coatings that reduce non-specificbonding of proteins or decrease other forms of “bio-fouling,” such as inmarine coatings.

The invention may be understood in conjunction with the followingnon-limiting examples.

Example 1A Synthesis ofBis[(n-butyldimethylsiloxy)polydimethylsiloxy](methacryloxypropyl)methylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 292.8 g (1.316 moles) ofhexamethylcyclotrisiloxane and 374.5 g of hexane. A half molarequivalent addition of n-butyllithium (460 ml of 1.64M hexane solution)was made rapidly through the addition funnel. An exotherm was observed(18.7° to 37.5° C.). Thereafter, cooling was used to maintain thetemperature below 40° C. The mixture was stirred for one hour and then107.3 g (1.468 moles) of dimethylformamide (DMF) were added at once. Aslight exotherm was observed, pot temperature rose from 24.0° to 29.5°C., and the mixture was stirred for four hours. The coupling reactionwas accomplished by adding 0.040 g of p-methoxyphenol (MEHQ), followedby the addition of 88.5 g of methacryloxypropylmethyldichlorosilane overfifteen minutes. Pot temperature rose from 21.7° to 33.2° C. The mixturechanged from clear to cloudy and was stirred for an additional 18 hours.Water (924 g) was added to the reaction mixture with stirring andagitated for 15 minutes. The contents of the flask were separated intoaqueous and non-aqueous layers in a separatory funnel and the aqueouslayer was discarded. The organic layer was dried over anhydrous sodiumsulfate, filtered, transferred to a rotary evaporator and stripped under10 mm Hg vacuum to a maximum pot temperature of 60° C. The resulting oil(367.5 g) had a theoretical molecular weight of 1085 Daltons, arefractive index (25°) of 1.4174, a density of 0.932 g/ml, and aviscosity of 9.2 cPs. GPC data (polystyrene st'd without correlation):Mn: 1215, Mw/Mn: 1.24. The structure of the final product is shown instructure (IV).

Example 1B Synthesis ofBis[(n-butyldimethylsiloxy)polydimethlsiloxy](methacryloxypropyl)methylsilane

This Example is a variation on Example 1A. A 3 L 4 neck flask equippedwith an overhead stirrer, pot thermometer, reflux condenser, water bathand addition funnel was blanketed with nitrogen and charged with 172.8 g(0.776 moles) of hexamethylcyclotrisiloxane and 401.4 g of hexane. Amolar equivalent addition of n-butyllithium (475 ml of 1.64M hexanesolution) was made rapidly through the addition funnel. An exotherm wasobserved (16.0° to 28.0° C.). Thereafter, cooling was used to maintaintemperature below 40° C. The mixture was stirred for one hour and then113.8 g (1.5568 moles) of dimethylformamide (DMF) were added at once. Aslight exotherm was observed, pot temperature rose from 19° to 26° C.,and the mixture was stirred for four hours. The coupling reaction wasaccomplished by adding 0.030 g of p-methoxyphenol (MEHQ), followed bythe addition of 93.4 g of methacryloxypropylmethyldichlorosilane overfifteen minutes. Pot temperature rose from 15° to 26° C. The mixturechanged from clear to cloudy and was stirred for an additional 18 hours.Water (976 g) was added to the reaction mixture with stirring andagitated for 30 minutes. The contents of the flask were separated intoaqueous and non-aqueous layers in a separatory funnel and the aqueouslayer was discarded. The organic layer was dried over anhydrous sodiumsulfate, filtered, transferred to a rotary evaporator and stripped under10 mm Hg vacuum to a maximum pot temperature of 60° C. The resulting oil(264 g) had a theoretical molecular weight of 730 Daltons, a refractiveindex (25°) of 1.4230, a density of 0.929 g/ml, and a viscosity of 5.9cPs. GPC data (polystyrene st'd without correlation)—Mn: 1012, Mw/Mn:1.183. The structure of the final product is shown in structure (IV).

Example 2 Synthesis ofTris[(n-butyldimethylsiloxy)polydimethylsiloxy]methacryloxypropylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser and addition funnel was blanketed with nitrogen andcharged with 175.2 g (0.787 moles) of hexamethylcyclotrisiloxane and394.4 g of hexane. A molar equivalent addition of n-butyllithium (490 mlof 1.64M hexane solution) was made rapidly through the addition funnel.An exotherm was observed (18.2° to 33.5° C.). Thereafter, cooling wasused to maintain the temperature below 40° C. The mixture was stirredfor one hour, and then 114.4 g (1.565 moles) of dimethylformamide (DMF)were added at once. A slight exotherm was observed, pot temperature rosefrom 24.6° to 30.2° C., and the mixture was stirred for four hours. Thecoupling reaction was accomplished by adding 0.03 g of p-methoxyphenol(MEHQ), followed by the addition of 64.0 g ofmethacryloxypropyltrichlorosilane over fifteen minutes. Pot temperaturerose from 20.4° C. to 28.7° C. The mixture changed from clear to cloudyand was stirred for an additional 18 hours. Water (995 g) was added tothe reaction mixture with stirring and agitated for 15 minutes. Thecontents of the flask were separated into aqueous and non-aqueous layersin a separatory funnel and the aqueous layer was discarded. The organiclayer was dried over anhydrous sodium sulfate, filtered, transferred toa rotary evaporator and stripped under 10 mm Hg vacuum to a maximum pottemperature of 60° C. The resulting oil (236.5 g) had a theoreticalmolecular weight of 994 Daltons, a refractive index (25°) of 1.4222, adensity of 0.918 g/ml, and a viscosity of 8.2 cPs. GPC data (polystyrenest'd without correlation)—Mn: 1090, Mw/Mn: 1.19. The structure of thefinal product is shown in structure (II).

Example 3 Synthesis ofBis[(t-butyldimethylsiloxypropyl)polydimethylsiloxy](methacryloxypropyl)methylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 65.3 g (0.2935 moles) ofhexamethylcyclotrisiloxane and 255.6 g of cyclohexane. A molarequivalent addition of 3-(t-butyldimethylsiloxy)-1-propyllithium (310 mlof 0.93M cyclohexane solution) was made rapidly through the additionfunnel. An exotherm was observed (20.5° to 30.5° C.). Thereafter,cooling was used to maintain temperature below 40° C. The mixture wasstirred for one hour, and then 42.8 g (0.5855 moles) ofdimethylformamide (DMF) were added at once. A slight exotherm wasobserved, pot temperature rose from 22.0° to 26.2° C., and the mixturewas stirred for 4 hours. The coupling reaction was accomplished byadding 0.040 g of p-methoxyphenol (MEHQ), followed by the addition of34.9 g of methacryloxypropylmethyldichlorosilane over fifteen minutes.Pot temperature rose from 18.4° to 31.3° C. The mixture changed fromclear to cloudy and was stirred for an additional 16 hours. Water (368.5g) was added to the reaction mixture with stirring and agitated for 90minutes. The contents of the flask were separated into aqueous andnon-aqueous layers in a separatory funnel and the aqueous layer wasdiscarded. The organic layer was dried over anhydrous sodium sulfate,filtered, transferred to a rotary evaporator and stripped under 10 mm Hgvacuum to a maximum pot temperature of 60° C. The resulting oil (129.5g) had a theoretical molecular weight of 960 Daltons, a refractive index(25°) of 1.4320, a density of 0.906 g/ml, and a viscosity of 17.2 cPs.GPC data (polystyrene st'd without correlation)—Mn: 1126, Mw/Mn: 1.139.The structure of the final product is shown in structure (VI).

Example 4 Synthesis ofBis[(t-butyldimethylsiloxypropyl)polydimethylsiloxy]methylhydrosilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 66.3 g (0.3681 moles) ofhexamethylcyclotrisiloxane and 252 g of cyclohexane. A molar equivalentaddition of 3-(t-butyldimethylsiloxy)-1-propyl lithium (350 ml of 0.93Mcyclohexane solution) was made rapidly through the addition funnel. Anexotherm was observed (17.8° to 24.0° C.). Thereafter, cooling was usedto maintain the temperature below 40° C. The mixture was stirred for onehour, and then 43.8 g (0.5992 moles) of dimethylformamide (DMF) wereadded at once. A slight exotherm was observed, pot temperature rose from20.6° to 25.1° C., and the mixture was stirred for four hours. Thecoupling reaction was accomplished by adding 17.0 g ofmethyldichlorosilane over fifteen minutes. Pot temperature rose from20.2° to 32.3° C. The mixture changed from clear to cloudy and wasstirred for an additional 16 hours. Water (372.5 g) was added to thereaction mixture with stirring and agitated for 30 minutes. The contentsof the flask were separated into aqueous and non-aqueous layers in aseparatory funnel and the aqueous layer was discarded. The organic layerwas dried over anhydrous sodium sulfate, filtered, transferred to arotary evaporator and stripped under 10 mm Hg vacuum to a maximum pottemperature of 60° C. The resulting oil (121.3 g) had a theoreticalmolecular weight of 836 Daltons, a refractive index (25°) of 1.4245, adensity of 0.8974 g/ml, and a viscosity of 10.6 cPs. GPC data(polystyrene st'd without correlation)—Mn: 878, Mw/Mn: 1.142. Thestructure of the final product is shown in structure (VII).

Example 5 Synthesis ofBis[(n-butyl)polytrifluoropropylmethylsiloxy](methacryloxypropyl)methylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 220.6 g (0.4708 moles) oftris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane and 253 g ofhexane. A molar equivalent addition of n-butyl lithium (280 ml of 1.64Mhexane solution) was made rapidly through the addition funnel. Anexotherm was observed (20.8° to 31.4° C.). Thereafter, cooling was usedto maintain the temperature below 40° C. The mixture was stirred for onehour, and then 68.5 g (0.9371 moles) of dimethylformamide (DMF) wereadded at once. A slight exotherm was observed, pot temperature rose from23.5° to 33.2° C., and the mixture was stirred for four hours. Thecoupling reaction was accomplished by adding 0.020 g of p-methoxyphenol(MEHQ), followed by the addition of 55.6 g ofmethacryloxypropylmethyldichlorosilane over fifteen minutes. Pottemperature rose from 19.2° to 36.5° C. The mixture changed from clearto cloudy and was stirred for an additional 18 hours. Water (582 g) wasadded to the reaction mixture with stirring and agitated for 15 minutes.The contents of the flask were separated into aqueous and non-aqueouslayers in a separatory funnel and the aqueous layer was discarded. Theorganic layer was dried over anhydrous sodium sulfate, filtered,transferred to a rotary evaporator and stripped under 10 mm Hg vacuum toa maximum pot temperature of 60° C. The resulting oil (262 g) had atheoretical molecular weight of 898 Daltons, a refractive index (25°) of1.3984, a density of 1.094 g/ml, and a viscosity of 52.3 cPs. GPC data(polystyrene st'd without correlation)—Mn: 1487, Mw/Mn: 1.095. Thestructure of the final product is shown in structure (VIII).

Example 6 Synthesis ofBis[(t-butyldimethylsiloxypropyl)polydimethylsiloxy]vinylmethylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 140.8 g (0.6328 moles) ofhexamethylcyclotrisiloxane and 344.4 g of cyclohexane. A half molarequivalent addition of 3-(t-butyldimethylsiloxy)-1-propyllithium (340 mlof 0.93M cyclohexane solution) was made rapidly through the additionfunnel. An exotherm was observed (10.5° to 31.2° C.). Thereafter,cooling was used to maintain temperature below 40° C. The mixture wasstirred for one hour, and then 50.7 g (0.6936 moles) ofdimethylformamide (DMF) were added at once. A slight exotherm wasobserved, pot temperature rose from 20.6° to 22.0° C., and the mixturewas stirred for four hours. The coupling reaction was accomplished byadding 22.8 g of vinylmethyldichlorosilane over fifteen minutes. Pottemperature rose from 17.8° to 30.6° C. The mixture changed from clearto cloudy and was stirred for an additional 16 hours. Water (351 g) wasadded to the reaction mixture with stirring and agitated for 90 minutes.The contents of the flask were separated into aqueous and non-aqueouslayers in a separatory funnel and the aqueous layer was discarded. Theorganic layer was dried over anhydrous sodium sulfate, filtered,transferred to a rotary evaporator and stripped under 10 mm Hg vacuum toa maximum pot temperature of 60° C. The resulting oil (194.2 g) had atheoretical molecular weight of 1300 Daltons, a refractive index (25°)of 1.4188, a density of 0.899, and a viscosity of 16.9 cPs. GPC data(polystyrene st'd without correlation)—Mn: 1348, Mw/Mn: 1.26. Thestructure of the final product is shown in structure (IX).

Example 7 Synthesis ofBis[(hydroxypropyldimethylsiloxy)polylmethylsiloxy]vinylmethylsilane

A 500 mL 3 neck flask equipped with an magnetic stirrer, potthermometer, reflux condenser, heating mantle and addition funnel wasblanketed with nitrogen and charged with 180 mL of a solution preparedfrom 29 g concentrated hydrochloric acid and 971 g of ethanol. 50 mL ofthe product of Example 6 were charged to the addition funnel and addedto the pot over a period of 16 minutes. The mixture turned hazyinitially, then cleared during the addition. The mixture was stirred at20-25° C. for 4.25 hours. 4.5 g of sodium bicarbonate was added toneutralize the mixture. The resulting salts were filtered off, and thefiltrate was stripped in a rotary evaporator under 10 mmHg vacuum and amaximum temperature of 80° C., removing ethanol andt-butyldimethylsilanol, and then filtered. The resulting oil (36.5 g)showed a peak in the FT-IR at 3335.69 cm⁻¹, corresponding to thehydroxyl groups formed on the endcaps of the PDMS chain. The structureof the final product is shown in structure (X).

Example 8A Synthesis ofBis[(n-butyldimethylsiloxy)polydimethylsiloxy]methylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 702.3 (3.16 moles) ofhexamethylcyclotrisiloxane and 1590 g of hexane. A molar equivalentaddition of n-butyllithium (1930 ml of 1.64M hexane solution) was maderapidly through the addition funnel. An exotherm was observed (14.1° to28.8° C.). Thereafter, cooling was used to maintain temperature below40° C. The mixture was stirred for one hour, and then 420 (5.75 moles)of dimethylformamide (DMF) were added at once. A slight exotherm wasobserved, pot temperature rose from 16.9° to 24.0° C., and the mixturewas stirred for four hours. The coupling reaction was accomplished byadding 183.8 g of methyldichlorosilane over fifteen minutes. Pottemperature rose from 19.1° to 39.2° C. The mixture changed from clearto cloudy and was stirred for an additional 18 hours. Water (3982 g) wasadded to the reaction mixture with stirring and agitated for 90 minutes.The contents of the flask were separated into aqueous and non-aqueouslayers in a separatory funnel and the aqueous layer was discarded. Theorganic layer was dried over anhydrous sodium sulfate, filtered,transferred to a rotary evaporator and stripped under 10 mm Hg vacuum toa maximum pot temperature of 60° C. The resulting oil (825 g) had atheoretical molecular weight of 590 Daltons, a refractive index (25°) of1.4086, a density of 0.985 g/ml, and a viscosity of 3.5 cPs. GPC data(polystyrene st'd without correlation)—Mn: 652, Mw/Mn: 1.20. Thestructure of the final product is shown in structure (XI).

Example 8B Synthesis ofBis[(n-butyldimethylsiloxy)polydimethylsiloxy]glycidoxypropylmethylsilane

A 200 mL 3 neck flask equipped with a magnetic stirrer, pot thermometer,reflux condenser, heating mantle and addition funnel was blanketed withnitrogen and charged with 75.5 g of product of Example 8A. The pot washeated to 85.4° C. and 1 g of allylglycidylether was added via syringealong with a catalytic amount of Karstedt's catalyst in xylenes. Another14.8 g of allylglycidylether was added dropwise from the addition funnelto the pot. An exotherm was observed from 85.4° C. to 100.6° C. An FT-IRscan of the resulting mixture confirmed that no Si—H remained. The potwas stripped to 110° C. and <10 mmHg. The resulting oil (84.5 g) had atheoretical molecular weight of 717 Daltons, a refractive index (25°) of1.4232, a density of 0.90779 g/ml, and a viscosity of 7.5 cPs. GPC data(polystyrene st'd without correlation)—Mn: 753, Mw/Mn: 1.22. Thestructure of the final product is shown in structure (XII).

Example 9 Synthesis ofα-(n-butyltrifluoropropylmethylsiloxy-ω-(methacryloxypropyl)dimethylsiloxyterminated poly(trifluoropropylmethyl)siloxane

A 5 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 989.8 g (2.112 moles) oftris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane and 720.8 g ofhexane. A half molar equivalent addition of n-butyllithium (645 ml of1.64M hexane solution) was made rapidly through the addition funnel. Anexotherm was observed (20.6° to 31.5° C.). Thereafter, cooling was usedto maintain the temperature below 40° C. The mixture was stirred for onehour, and then 67.1 g (0.92 moles) of dimethylformamide (DMF) were addedat once. A slight exotherm was observed, pot temperature rose from 18.4°to 28.9° C., and the mixture was stirred for four hours. The cappingreaction was accomplished by adding 0.040 g of p-methoxyphenol (MEHQ),followed by the addition of 233.7 g ofmethacryloxypropyldimethylchlorosilane over 20 minutes. Pot temperaturerose from 19.2° to 25.9° C. The mixture changed from clear to cloudy andwas stirred for an additional 16 hours. Water (1032 g) was added to thereaction mixture with stirring and agitated for 15 minutes. The contentsof the flask were separated into aqueous and non-aqueous layers in aseparatory funnel and the aqueous layer was discarded. The organic layerwas dried over anhydrous sodium sulfate, filtered, transferred to arotary evaporator and stripped under 10 mm Hg vacuum to a maximum pottemperature of 60° C. The resulting oil (1043 g) had a theoreticalmolecular weight of 855.5 Daltons, a refractive index (25°) of 1.3959, adensity of 1.1559 g/ml, and a viscosity of 62.2 cPs. GPC data(polystyrene st'd without correlation): Mn: 1662, Mw/Mn: 1.454. Thefinal product had structure (XIII).

Example 10 Synthesis ofBis[(hydroxydimethylsiloxy)polydimethylsiloxy]methacryloxypropylmethylsilane

A 500 mL 3 neck flask equipped with a magnetic stirrer, pot thermometer,reflux condenser, heating mantle, and addition funnel was blanketed withnitrogen and charged with 180 mL of a solution prepared from 29 gconcentrated hydrochloric acid and 971 g of ethanol. 50 mL of theproduct of Example 5 were charged to the addition funnel and added tothe pot over a period of 16 minutes. The mixture turned hazy initially,then cleared during the addition. The mixture was stirred at 20-25° C.for 1 hour. 4.8 g of sodium bicarbonate was added to neutralize themixture. The resulting salts were filtered off, and the filtrate wasstripped in a rotary evaporator under 10 mmHg vacuum and a maximumtemperature of 70° C., removing ethanol and t-butyldimethylsilanol, andthen filtered. The resulting oil (40.8 g) showed a peak in the FT-IR at3347.31 cm⁻¹ corresponding to the hydroxyl group formed on the endcapsof the PDMS chain.

Example 11 Synthesis ofBis[(n-butytrifluoropropylmethylsiloxy)poly(trifluoropropylmethylsiloxane)-block-poly(dimethylsiloxy](methacryloxypropyl)methylsilane

A 5 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel was blanketed withnitrogen and charged with 695.2 g (1.484 moles) of(3,3,3-trifluoropropyl)methylcyclotrisiloxane and 418 g of hexane. Amolar equivalent addition of n-butyllithium (930 ml of 1.60M hexanesolution) was made rapidly through the addition funnel. An exotherm wasobserved (16.7° to 41.6° C.). Thereafter cooling was used to maintaintemperature below 40° C. The mixture was stirred for one hour and then217 g (2.968 moles) of dimethylformamide (DMF) were added at once. Anexotherm was observed, pot temperature rose from 20.3° to 38.9° C., andthe mixture was stirred for two hours. Then, 336.1 g (1.511 moles) ofhexamethylcylcotrisiloxane dissolved in 372 g of hexane were added, pottemperature rose from 20.9° to 21.3° C., and the mixture was stirred forthree hours. The coupling reaction was accomplished by adding 0.15 g ofp-methoxyphenol (MEHQ) followed by the addition of 179.2 g ofmethacryloxypropylmethyldichlorosilane over 10 minutes. Pot temperaturerose from 22.5° to 35.9° C. The mixture changed from clear to cloudy andwas stirred for an additional 16 hours. Water (300 g) was added to thereaction mixture with stirring and agitated for 15 minutes. The contentsof the flask were separated into aqueous and non-aqueous layers in aseparatory funnel and the aqueous layer was discarded. The organic layerwas dried over anhydrous sodium sulfate, filtered, transferred to arotary evaporator and stripped under 10 mmHg vacuum to a maximum pottemperature of 60° C. The resulting oil (1057 g) had a theoreticalmolecular weight of 1343 Daltons, a refractive index (25°) of 1.3991, adensity of 1.094 g/ml and a viscosity of 35.8 cPs. GPC data (polystyrenest'd without correlation): Mn: 1729, Mw/Mn: 1.28. The final product hadthe structure (XIV).

Example H-1 Hypothetical Example Synthesis ofBis[(phenyldimethylsiloxy)polydimethylsiloxy]vinylmethylsilane

A 3 L 4 neck flask equipped with an overhead stirrer, pot thermometer,reflux condenser, water bath and addition funnel is blanketed withnitrogen, and is charged with 333.0 g (1.5 moles) ofhexamethylcyclotrisiloxane, and heated to 80° C. A half molar equivalentaddition of phenyllithium (290 ml of 2.6M in cyclohexane solution) isthen added rapidly through the addition funnel. The mixture is agitateduntil homogeneous and then 2 ml of diglyme are added. An exotherm isobserved (100° to 135° C.). The mixture is stirred for four hourswithout heating. 125 ml of toluene are added and then the mixture isheated to 60° C. and stirred until the mixture appears homogeneous andthen is allowed to cool to 40-45° C. The coupling reaction isaccomplished by adding 0.040 g of p-methoxyphenol (MEHQ), followed bythe addition of methacryloxypropylmethyldichlorosilane. The mixturechanges from clear to cloudy and is stirred for an additional 16 hours.Water (500 g) is added to the reaction mixture with stirring andagitated for 15 minutes. The contents of the flask are separated intoaqueous and non-aqueous layers in a separatory funnel and the aqueouslayer is discarded. The mixture is agitated a second time with water.The organic layer is dried over anhydrous sodium sulfate, filtered,transferred to a rotary evaporator and stripped under 10 mm Hg vacuum toa maximum pot temperature of 60° C.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

1. A symmetric siloxane macromonomer comprising a low molecular weightsiloxane polymer having two or three monomer termini and onepolymerizable functional group, wherein the polymerizable functionalgroup is located equidistant from each of the two or three monomertermini and wherein the two or three monomer termini are polar andhydrophilic.
 2. The symmetric siloxane macromonomer according to claim1, wherein the polymerizable functional group is selected from the groupconsisting of vinyl, methacryloxyalkyl, acryloxyalkyl, arylamidoalkyl,and styryl.
 3. The symmetric siloxane macromonomer according to claim 1,wherein the polar and hydrophilic termini comprise groups selected fromthe group consisting of hydroxyl, ether, and polyether groups.
 4. Thesymmetric silxoane macromonomer according to claim 1, wherein thesiloxane polymer has a molecular weight of less than about 20,000Daltons.
 5. The symmetric siloxane macromonomer according to claim 1,wherein the siloxane polymer has a molecular weight of less than about10,000 Daltons.
 6. The symmetric siloxane macromonomer according toclaim 1, wherein the siloxane polymer has a molecular weight of about500 to about 5,000 Daltons.
 7. The symmetric siloxane macromonomeraccording to claim 1, wherein the siloxane macromonomer comprises asubstituted or unsubstituted polyalkylmethylsiloxane backbone.
 8. Thesymmetric siloxane macromonomer according to claim 1, wherein thesiloxane macromonomer comprises a polydimethylsiloxane backbone.
 9. Thesymmetric siloxane macromonomer according to claim 1, wherein thesiloxane macromonomer comprises a backbone selected from the groupconsisting of a fluorinated polyalkylmethylsiloxane backbone, apolydiphenylsiloxane backbone, and a polyphenylmethylsiloxane backbone.10. The symmetric siloxane macromonomer according to claim 1, whereinthe siloxane macromonomer comprises a backbone comprising at least twodifferent blocks.
 11. A biocompatible material comprising themacromonomer according to claim 1, wherein the two or three monomertermini comprise hydroxyl groups.
 12. The material according to claim11, wherein the macromonomer has structure (V)

wherein n is the degree of polymerization.
 13. The symmetric siloxanemacromonomer according to claim 1, wherein the macromonomer comprisesthree monomer termini.
 14. A symmetric siloxane macromonomer comprisinga low molecular weight siloxane polymer having two or three monomertermini and one polymerizable functional group, wherein thepolymerizable functional group is located equidistant from the two orthree monomer termini, and wherein the two or three monomer termini arenon-polar and hydrophobic and comprise functional groups selected fromthe group consisting of alkyl and aryl groups with the proviso that,where the functional groups are alkyl groups, at least one of them mustbe other than a methyl group.
 15. The symmetric siloxane macromonomeraccording to claim 14, wherein the polymerizable functional group isselected from the group consisting of vinyl, methacryloxyalkyl,acryloxyalkyl, arylamidoalkyl, and styryl.
 16. The symmetric silxoanemacromonomer according to claim 14, wherein the siloxane polymer has amolecular weight of less than about 20,000 Daltons.
 17. The symmetricsiloxane macromonomer according to claim 14, wherein the siloxanepolymer has a molecular weight of less than about 10,000 Daltons. 18.The symmetric siloxane macromonomer according to claim 14, wherein thesiloxane polymer has a molecular weight of about 500 to about 5,000Daltons.
 19. The symmetric siloxane macromonomer according to claim 14,wherein the siloxane macromonomer comprises a substituted orunsubstituted polyalkylmethylsiloxane backbone.
 20. The symmetricsiloxane macromonomer according to claim 14, wherein the siloxanemacromonomer comprises a polydimethylsiloxane backbone.
 21. Thesymmetric siloxane macromonomer according to claim 14, wherein thesiloxane macromonomer comprises a backbone selected from the groupconsisting of a fluorinated polyalkylmethylsiloxane backbone, apolydiphenylsiloxane backbone, and a polyphenylmethylsiloxane backbone.22. The symmetric siloxane macromonomer according to claim 14, whereinthe siloxane macromonomer comprises a backbone comprising at least twodifferent blocks.
 23. The symmetric siloxane macromonomer according toclaim 14, wherein the siloxane polymer comprises three monomer termini.24. The symmetric siloxane macromonomer according to claim 23, whereinthe macromonomer has structure (II):

wherein n is the degree of polymerization.